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    <title>Image Load Events</title>
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          <h4 id="title">Image Load Events</h4>
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  <div id="map" class="map"></div>
  <div id="progress"></div>
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          <p id="shortdesc">Example using image load events.</p>
          <div id="docs"><p>Image sources fire events related to image loading.  You can listen for <code>imageloadstart</code>, <code>imageloadend</code>, and <code>imageloaderror</code> type events to monitor image loading progress.  This example registers listeners for these events and renders an image loading progress bar at the bottom of the map.</p>
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          <div id="api-links">Related API documentation: <ul class="inline"><li><a href="../apidoc/ol.Map.html" title="API documentation for ol.Map">ol.Map</a></li>,<li><a href="../apidoc/ol.View.html" title="API documentation for ol.View">ol.View</a></li>,<li><a href="../apidoc/ol.layer.Image.html" title="API documentation for ol.layer.Image">ol.layer.Image</a></li>,<li><a href="../apidoc/ol.source.ImageWMS.html" title="API documentation for ol.source.ImageWMS">ol.source.ImageWMS</a></li></ul></div>
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        <form method="POST" id="codepen-form" target="_blank" action="https://codepen.io/pen/define/">
          <textarea class="hidden" name="title">Image Load Events</textarea>
          <textarea class="hidden" name="description">Example using image load events.</textarea>
          <textarea class="hidden" name="js">/**
 * Renders a progress bar.
 * @param {Element} el The target element.
 * @constructor
 */
function Progress(el) {
  this.el &#x3D; el;
  this.loading &#x3D; 0;
  this.loaded &#x3D; 0;
}


/**
 * Increment the count of loading tiles.
 */
Progress.prototype.addLoading &#x3D; function() {
  if (this.loading &#x3D;&#x3D;&#x3D; 0) {
    this.show();
  }
  ++this.loading;
  this.update();
};


/**
 * Increment the count of loaded tiles.
 */
Progress.prototype.addLoaded &#x3D; function() {
  var this_ &#x3D; this;
  setTimeout(function() {
    ++this_.loaded;
    this_.update();
  }, 100);
};


/**
 * Update the progress bar.
 */
Progress.prototype.update &#x3D; function() {
  var width &#x3D; (this.loaded / this.loading * 100).toFixed(1) + &#x27;%&#x27;;
  this.el.style.width &#x3D; width;
  if (this.loading &#x3D;&#x3D;&#x3D; this.loaded) {
    this.loading &#x3D; 0;
    this.loaded &#x3D; 0;
    var this_ &#x3D; this;
    setTimeout(function() {
      this_.hide();
    }, 500);
  }
};


/**
 * Show the progress bar.
 */
Progress.prototype.show &#x3D; function() {
  this.el.style.visibility &#x3D; &#x27;visible&#x27;;
};


/**
 * Hide the progress bar.
 */
Progress.prototype.hide &#x3D; function() {
  if (this.loading &#x3D;&#x3D;&#x3D; this.loaded) {
    this.el.style.visibility &#x3D; &#x27;hidden&#x27;;
    this.el.style.width &#x3D; 0;
  }
};

var progress &#x3D; new Progress(document.getElementById(&#x27;progress&#x27;));

var source &#x3D; new ol.source.ImageWMS({
  url: &#x27;https://ahocevar.com/geoserver/wms&#x27;,
  params: {&#x27;LAYERS&#x27;: &#x27;topp:states&#x27;},
  serverType: &#x27;geoserver&#x27;
});

source.on(&#x27;imageloadstart&#x27;, function() {
  progress.addLoading();
});

source.on(&#x27;imageloadend&#x27;, function() {
  progress.addLoaded();
});
source.on(&#x27;imageloaderror&#x27;, function() {
  progress.addLoaded();
});

var map &#x3D; new ol.Map({
  logo: false,
  layers: [
    new ol.layer.Image({source: source})
  ],
  target: &#x27;map&#x27;,
  view: new ol.View({
    center: [-10997148, 4569099],
    zoom: 4
  })
});
</textarea>
          <textarea class="hidden" name="css">.map {
  background: #E0ECED;
}
.wrapper {
  position: relative;
}
#progress {
  position: absolute;
  bottom: 0;
  left: 0;
  height: 2px;
  background: rgba(0, 60, 136, 0.4);
  width: 0;
  transition: width 250ms;
}</textarea>
          <textarea class="hidden" name="html">&lt;div class&#x3D;&quot;wrapper&quot;&gt;
  &lt;div id&#x3D;&quot;map&quot; class&#x3D;&quot;map&quot;&gt;&lt;/div&gt;
  &lt;div id&#x3D;&quot;progress&quot;&gt;&lt;/div&gt;
&lt;/div&gt;
</textarea>
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          <input type="hidden" name="data">
        </form>
        <pre><code id="example-source" class="language-markup">&lt;!DOCTYPE html&gt;
&lt;html&gt;
  &lt;head&gt;
    &lt;title&gt;Image Load Events&lt;/title&gt;
    &lt;link rel="stylesheet" href="https://openlayers.org/en/v4.6.5/css/ol.css" type="text/css"&gt;
    &lt;!-- The line below is only needed for old environments like Internet Explorer and Android 4.x --&gt;
    &lt;script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=requestAnimationFrame,Element.prototype.classList,URL"&gt;&lt;/script&gt;
    &lt;script src="https://openlayers.org/en/v4.6.5/build/ol.js"&gt;&lt;/script&gt;
    &lt;style&gt;
      .map {
        background: #E0ECED;
      }
      .wrapper {
        position: relative;
      }
      #progress {
        position: absolute;
        bottom: 0;
        left: 0;
        height: 2px;
        background: rgba(0, 60, 136, 0.4);
        width: 0;
        transition: width 250ms;
      }    &lt;/style&gt;
  &lt;/head&gt;
  &lt;body&gt;
    &lt;div class&#x3D;&quot;wrapper&quot;&gt;
      &lt;div id&#x3D;&quot;map&quot; class&#x3D;&quot;map&quot;&gt;&lt;/div&gt;
      &lt;div id&#x3D;&quot;progress&quot;&gt;&lt;/div&gt;
    &lt;/div&gt;
    &lt;script&gt;
      /**
       * Renders a progress bar.
       * @param {Element} el The target element.
       * @constructor
       */
      function Progress(el) {
        this.el &#x3D; el;
        this.loading &#x3D; 0;
        this.loaded &#x3D; 0;
      }


      /**
       * Increment the count of loading tiles.
       */
      Progress.prototype.addLoading &#x3D; function() {
        if (this.loading &#x3D;&#x3D;&#x3D; 0) {
          this.show();
        }
        ++this.loading;
        this.update();
      };


      /**
       * Increment the count of loaded tiles.
       */
      Progress.prototype.addLoaded &#x3D; function() {
        var this_ &#x3D; this;
        setTimeout(function() {
          ++this_.loaded;
          this_.update();
        }, 100);
      };


      /**
       * Update the progress bar.
       */
      Progress.prototype.update &#x3D; function() {
        var width &#x3D; (this.loaded / this.loading * 100).toFixed(1) + &#x27;%&#x27;;
        this.el.style.width &#x3D; width;
        if (this.loading &#x3D;&#x3D;&#x3D; this.loaded) {
          this.loading &#x3D; 0;
          this.loaded &#x3D; 0;
          var this_ &#x3D; this;
          setTimeout(function() {
            this_.hide();
          }, 500);
        }
      };


      /**
       * Show the progress bar.
       */
      Progress.prototype.show &#x3D; function() {
        this.el.style.visibility &#x3D; &#x27;visible&#x27;;
      };


      /**
       * Hide the progress bar.
       */
      Progress.prototype.hide &#x3D; function() {
        if (this.loading &#x3D;&#x3D;&#x3D; this.loaded) {
          this.el.style.visibility &#x3D; &#x27;hidden&#x27;;
          this.el.style.width &#x3D; 0;
        }
      };

      var progress &#x3D; new Progress(document.getElementById(&#x27;progress&#x27;));

      var source &#x3D; new ol.source.ImageWMS({
        url: &#x27;https://ahocevar.com/geoserver/wms&#x27;,
        params: {&#x27;LAYERS&#x27;: &#x27;topp:states&#x27;},
        serverType: &#x27;geoserver&#x27;
      });

      source.on(&#x27;imageloadstart&#x27;, function() {
        progress.addLoading();
      });

      source.on(&#x27;imageloadend&#x27;, function() {
        progress.addLoaded();
      });
      source.on(&#x27;imageloaderror&#x27;, function() {
        progress.addLoaded();
      });

      var map &#x3D; new ol.Map({
        logo: false,
        layers: [
          new ol.layer.Image({source: source})
        ],
        target: &#x27;map&#x27;,
        view: new ol.View({
          center: [-10997148, 4569099],
          zoom: 4
        })
      });
    &lt;/script&gt;
  &lt;/body&gt;
&lt;/html&gt;</code></pre>
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